Problem: If $a + 4b = 3$ and $4x + 7y + 8z = -4$, what is $7a + 32z + 16x + 28y + 28b$ ?
Answer: $= 7a + 28b + 16x + 28y + 32z$ $= (7) \cdot (a + 4b) + (4) \cdot (4x + 7y + 8z)$ $= (7) \cdot (3) + (4) \cdot (-4)$ $= 21 - 16$ $= 5$